"Devoted to Spouse" Aspiration

I would like something like this whether it was a trait or an aspiration. I never break up marriages in my game and if I know that 2 sims are a "couple" even if they're not married, I don't allow my sim to get flirty with them. I never use the "unflirty" trait because I'm always afraid it will also prevent my sim from being flirty with their significant other. Maybe a monogamous trait might work so if a sim is in a relationship they would be devoted to that sim.